I've spent 5 minutes Googling - I guess you'll have spent longer, so I won't continue.

If there's no other clever ideas from the forum, one thing you could consider is this,

Connect your stepper, wind the pot control to CCW limit. try stepping the motor (if the minimum current is CCW, max CW - which is logic) - it may or may not turn. Rotate the pot CW until the motor is spinning reliably, then leave stepping for 5 minutes, monitoring motor temperature. Continue to rotate the pot bit-by-bit and running the stepper for 5 minutes at a time. I saw a post on here recently by a respected member that suggested a stepper should operate upto an uncomfortable-to-hold temperature (60C, I think was mentioned). If you're running less than this then you can probably afford to up-the-current. What you're looking for is not necessarily 2A, but a safe operating temperature that is neither lifeing the motor or saturating the core. The motor doesn't really care if it has 2.000A or whatever flowing through it - it's looking to generate a magnetic force (proportional to current) without damaging the insulation on the coil through over-temperature.

Another method would be to replace the stepper with 2 10W, 1R resistors and step the driver until you get maximum potential across one resistor, and read-off the current (I = V, given a 1R resistor) - but that method is fraught with problems if there is a stepped current (positional current and hold current) and/or if the output drive is switched-mode (which I think it is, having seen an internal image on a chinese website) - again, think of the problem space - not to set the current to a specific value, but rather to set the current to keep the motors operating within their thermal range.